The up front cost of icemaker/dispeners?carbonator is high but the cost of electricity, water, and CO2 tanks is basically nothing on a per drink basis. Just think about everything that went into the factory which makes that syrup, the factory that makes the syrup bag, and all the logistics that deliver the finished product to the store. Then remember that costs pennies per drink. Even if all the other costs associated with that soda cost as much on a per drink basis, we're still talking ~10-20 cents per drink. Assuming every input cost is on the same scale also makes for a huge overestimate.

When I was a teenager I heard 17c for the cup, < 1c for the soda.

Of course they go for like $1.50 so no matter how it breaks down, it's a nice ROI.

I've heard stories of fast food places which say you can drink as much from the soda machines as you like, just don't put it in a cardboard cup.